1. Field of the invention
The present invention generally relates to electrophotography and more in particular to an electrostatic latent image developing device for use in developing electrostatic latent images formed on the surface of an electrostatic image support member in an electrophotographic process.
2. Description of the prior art
In electrostatic latent image developing devices it is known to transport the developing material which is supported in the form of a magnetic brush, on the outer peripheral surface of a developing sleeve in a circumferential direction of said sleeve so as to develop an electrostatic latent image formed on an electrostatic latent image support member by causing the developing material to rub against the surface of said support member at a developing region where said developing sleeve and said electrostatic latent image support member confront each other.
The developing material is supplied to the rear side of the developing sleeve opposite from the developing region thereof, and at the time it is picked up by the sleeve the developing material (usually composed of a mixture of carrier and toner) must be fully mixed and stirred, with toner particles therein being sufficiently triboelectrically charged, and sufficiently uniformly distributed along the length of the sleeve.
In order to satisfactorily mix and stir the developing material, it is known to use neighbouring feeding passages through which the developing material is fed in opposed directions by means of a sleeve incorporated with a magnet roller disposed in each feeding passage, thereby to circulate the developing material through end openings in a partition wall which separates the feeding passages. This arrangement is disclosed in Japanese Patent No. 1,068,753 to Kokkosho.
Since the feed passages are disposed in parallel relation to each other, and since end portions of the feeding passages are closed in the feeding direction to be accumulated in stopped, the developing material tends to be excessively large amounts downstream of the feeding direction in each feed passage, and in undesirable small amounts upstream thereof, and therefore deviation in the amount of the developing material takes place in the axial direction of the developing sleeve, thus leading to uneven development across the width of the developed image.
This problem has been recognized in U.S. Pat. No. 4,721,982 to Minolta, and in said patent an electrostatic latent image developing apparatus is disclosed in which two adjacent feeding passages are disposed in a non-parallel relation to each other.
This measure complicates the construction of the device since the rotating feed means of at least one feed channel is mounted in a tilted position which necessitates the provision of bearings the axis of which is not normal to the sidewall of the apparatus, and also gear wheels that are inclined to the vertical, and that must co-operate with other gear wheels that are rotating in a truly vertical plane.
Further, the buckets of the supply roller in this device are arranged outside of the helical vane or vane sections that produce the axial transport of the developing material through the feed passage. We have found that the axial feeding function in suchlike arrangement may become unsatisfactory, in particular in case the developing composition comprises a carrier based on ferrites and the toner particles are very fine, since this kind of developer mixture lends itself less readily to axial transport by screw means.